The thing with Bitcoin is I think it is very unlikely to drop much in the long term but quite likely to rise. If you want to buy more for short term gains then it is a risky strategy but if this is a medium to longer term investment than you will probably be fine. You can choose a pull back to get in, ie when it slightly drops each time on the way up. Watch 'node investor' on youtube for more info on the technicals of this, his most recent video covers it.